An essential consequence of multi-cellularity is the need for intercellular and tissue wide communication. As seen with animals, higher plants coordinate metabolic and developmental processes via signals transferred to different body parts. Plants use a dual vascular system consisting of phloem and xylem for long-distance transfer of metabolites and signalling molecules. In contrast to circular systems in animals, transport in flowering plants occurs in the phloem via the cytoplasm of connected cells devoid of nuclei. In addition to small molecules, a remarkably large number of so-called mobile micro RNAs (miRNAs), messenger RNAs (mRNAs), and phloem RNA-binding proteins (RBPs) were identified in the phloem and in chimeric plants. Mobile RNAs and RBPs move through plasmodesmata into and through the phloem to distinct tissues. Thus, mobile RNAs represent an additional class of signalling molecules, raising important questions in the field of intercellular signalling. This project combines the expertise of three research groups in the fields of cell biology/macromolecular transport, mathematical modelling/bioinformatics and phloem function/protein biochemistry. It addresses the questions: How are mobile miRNAs and mRNAs selected for transport? Is this process specific and regulated by RBPs and motifs? What determines their destination? And importantly, how are these signals processed in the destination cells? To address these questions, we will develop predictive models, using novel single cell transcriptomics pipelines to establish cell-type specific RNA transport and motifs (WP1), and studying the structure, affinity, and functions of phloem RBPs to gain insights in the RNA delivery mechanism (WP2). We will combine the advantages of the agronomically important plant oilseed rape to identify phloem RNAs and RBPs with the well-established A. thaliana model that allows us to identify and test cell-specific transported RNA signals and RBPs in a time-efficient manner.
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